Japanese phrase
___の理由は何ですか？ ___ no ri yū wa nan de su ka
Meaning
What is the reason behind ___?
When to use it
A polite question about why something happened or was done. It seeks a clear explanation and can sound direct in a formal setting.
Example dialogue
遅刻の理由は何ですか？ chi koku no ri yū wa nan de su ka
What is the reason behind the delay?
電車が遅れたからです。 den sha ga oku re ta ka ra de su
Because the train was late.